An OLED is a self-emissive device using a phenomenon generating light itself by combining electron and hole in a light-emitting layer if current is applied to a device including a fluorescent light-emitting layer or a phosphor light-emitting layer between its cathode and anode. The OLED is simple in a structure and a manufacturing process as well as can implement high definition image and wide viewing angle. Also, the OLED can completely implement moving picture and high color purity and has features suitable for portable electronic equipment due to low power consumption and low voltage operation.
The OLED has a multi-layer structure without using only the light-emitting layer between two electrodes in order to improve efficiency and lower operation voltage associated with the lifetime of a current device. The OLED generally has a multi-layer structure such as, for example, a hole injection and transfer layer, an electron injection and transfer layer, and a hole blocking layer, etc. The OLED forms exciton by recombining the electron and the hole injected from each of the cathode and anode in the light-emitting layer and uses light generated by the exciton energy loss. In the device, the thickness of each layer formed of organic matter is generally about 100 nm, high brightness light-emitting can be made under low voltage below 10V, and since the self-emission of fluorescence or phosphorescence is used, a rapid response speed for an input signal can be obtained.
In order to operate the OLED at low operating voltage, an energy barrier between the electrode and the organic matter should be lowered. In order to increase light-emitting efficiency, many electrons-holes should equally be injected in an applied voltage and the recombination probability thereof should be increased. In the case of the organic matter, high voltage is applied so that an organic light-emitting layer with weak molecular structure is damaged due to high energy, thereby deteriorating device's characteristic and lifetime. Therefore, it is very important to be able to inject a sufficient number of holes and electrons at low voltage.
Generally, in the case of the organic matter used in the light-emitting layer, the characteristics are deteriorated by holes. In order to prevent this phenomenon, the insertion of the hole blocking layer and/or the electron blocking layer has been used. An OLED comprising a layer formed of organic compounds containing 3-phenylindolyl group between the hole transfer layer and the light-emitting layer is disclosed in U.S. Pat. No. 6,670,053, the content introducing inorganic matter layer, such as Se, Te, ZnSe, etc., between the light-emitting layer and the hole blocking layer is disclosed in K.R. Patent No. 2006-0012120, and the content inserting an organic layer of LiF, NaF, etc. between a hole injection layer and a hole transfer layer is disclosed in K.R. Patent No. 2006-0078358. However, it is hard to find an example introducing an inorganic matter layer into the inside of the light-emitting layer. Furthermore, there has been a limitation in obtaining satisfactory efficiency and lifetime in the case of a conventional OLED structure using an organic matter intermediate layer formed.
Therefore, the present invention is the outcome of continuous study in order to solve several problems of the OLED. In other words, the present invention provides a method capable of considerably lowering the operating voltage and efficiency of OLED by a simple method of forming the inorganic oxide interlayer configured of at least one layer between the light-emitting layers, and in particular has the features capable of easily applying the method to an existing deposition process as well as a solution process suitable for a large size OLED.